Memory component with command-triggered data clock distribution

ABSTRACT

An integrated circuit includes a physical layer interface having a control timing domain and a data timing domain, and circuits that enable the control timing domain during a change in power conservation mode in response to a first event, and that enable the data timing domain in response to a second event. The control timing domain can include interface circuits coupled to a command and address path, and the data timing domain can include interface circuits coupled to a data path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/032,633 filed Jul. 11, 2018 (now U.S. Pat. No. 10,665,289), which isa continuation of U.S. patent application Ser. No. 15/616,209 filed Jun.7, 2017 (now U.S. Pat. No. 10,026,466), which is a continuation of U.S.patent application Ser. No. 15/242,423 filed Aug. 19, 2016 (now U.S.Pat. No. 9,704,560), which is a continuation of U.S. patent applicationSer. No. 14/799,362 filed Jul. 14, 2015 (now U.S. Pat. No. 9,430,027),which is a continuation of U.S. patent application Ser. No. 13/980,368filed Sep. 6, 2013 (now U.S. Pat. No. 9,098,281), which is a 35 U.S.C. §371 U.S. National Stage of International Patent Application No.PCT/US2012/028289 filed Mar. 8, 2012, which claims priority to U.S.Provisional Patent Application No. 61/451,023 filed Mar. 9, 2011. Eachof the foregoing patent applications is hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates generally to the field of integratedcircuits, and to power management technologies during events likepower-down exit for such devices.

BACKGROUND

Modern integrated circuits often include power management modes used forconservation of power. For example, many devices implement a power-downmode in which the integrated circuit conserves power by deactivatinginput and output buffers, excluding certain buffers for signals neededfor exiting the power-down mode. On exiting the power-down mode, thebuffers are reactivated and the clock, addresses and decoded commandsare distributed to the necessary elements of the device.

Many designs now operate with faster and slower clocks in respectivedomains on the device. Memory devices for example often include a clock,called a control clock herein, used for command and address logic andother functions on the device, and a data clock used for driving highspeed data path circuits and data interfaces on the device. The dataclock in such systems may run at a higher frequency than the controlclock. Recovery from a power-down mode, and other operations changingpower management modes for such devices, can require reactivatingcircuits in both the control clock domain and circuits in the data clockdomain.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a block diagram of an integrated circuit, including powermanagement circuits, as described herein, and a plurality of clockdomains in a physical layer interface.

FIG. 2 is a simplified diagram of a memory integrated circuit, includinga physical layer interface having a control clock domain and a dataclock domain, with different activation logic in each domain.

FIG. 3 is a simplified diagram of a physical layer interface for amemory device, such as a high speed synchronous dynamic random accessmemory, having a control clock CK domain and a higher speed data clockDCK domain, and power-down exit activation circuits enforcing differenttiming in the two domains.

FIG. 4 is a timing diagram illustrating a power-down exit operationaccording to a first logical architecture.

FIG. 5 is a timing diagram illustrating a power-down exit operationaccording to a second logical architecture.

FIG. 6 is a timing diagram illustrating a power-down exit operationaccording to a third logical architecture.

FIG. 7 is a timing diagram illustrating a power-down exit operationaccording to a fourth logical architecture.

FIG. 8 is a block diagram of a DRAM interface, including separate dataclock and control clock enable circuits operable on exit from apower-down mode.

FIG. 9 is a block diagram of a DRAM interface, including a data clockenable circuit including an external data clock enable signal, operableon exit from a power-down mode.

FIG. 10 is a block diagram of a DRAM interface, including a data clockenable circuit responsive to a command decoder, operable on exit from apower-down mode.

FIG. 11 illustrates a command/address sequence including a “shortcommand” which can be used as an event to signal activation of datadomain interface circuits.

FIG. 12 illustrates a alternative command/address sequence including amodified or dedicated command packet which can be used as both an eventto signal activation of data domain interface circuits and a command foran operation requiring such activation.

FIG. 13 is a block diagram of a multi-rank memory system includinglogical or physical data clock enable signals for data clock domainmanagement.

DETAILED DESCRIPTION

FIG. 1 is a simplified block diagram of an integrated circuit 10 havinga plurality of timing domains in its physical layer interface circuitry,and power management circuits which control enablement of timing signalsin the clock domains. So for a simplified example, an integrated circuit10 includes a data channel interface for a bus 15, having at least onecontrol line 15A (e.g. bus address and control lines) operating with afirst timing regime, and having at least one data line 15B (e.g. busdata lines) operating with a second timing regime. The integratedcircuit 10 has a first group 11 of one or more circuits in a firsttiming domain (Timing Domain A) to process a command and address signal,and which interfaces signals in the first timing regime on the busline(s) 15A with a memory core, and a second group 12 of one or morecircuits operating in second timing domain (Timing Domain B) to processa data signal, and which interfaces signals in the second timing regimeon the bus line(s) 15B with the memory core. Use of the timing signalsin the first and second groups 11, 12, is enabled and disabled by powermanagement logic 14 on the device according to power management modes byapplying a first enable signal to the first group 11, and a secondenable signal to the second group. At least one mode implemented by thepower management logic 14 causes one of the first and second groups tobe enabled to use its timing signals to support memory transactions onthe bus 15, while the other is not enabled for the same memorytransaction, or not enabled for at least a portion of the same memorytransaction.

The first and second timing regimes on the bus 15 and first and secondgroups 11, 12 of circuits on the integrated circuit 10 can operate inresponse to timing signals comprising first and second clock signals, orother signals that provide timing references for the interface betweenthe bus and IC core circuits. The first and second timing signals can beprovided by external sources. Alternatively, one of the timing signalscan be provided by an external source, and the other of the timingsignals can be derived from the externally-sourced timing signal. Insome examples, one of the timing signals can be generated using a clockdivider as a function of the other timing signal. In other examples,where a quadrature clock is used as one of the timing signals, one phaseof the quadrature clock can be used as the other timing signal. Also,both timing signals can be generated on the integrated circuit 10 usingseparate on-chip circuits. Other timing signal generation schemes can beused as appropriate for particular applications of the technology.

The architecture illustrated in FIG. 1 can be applied to memory devices,such as synchronous dynamic random access memory SDRAM devices, as wellas other classes of integrated circuits operating with buses thatinclude multiple timing regimes. Exemplary integrated circuits includingthe architecture illustrated in FIG. 1 include so-called system on achip devices that integrate memory arrays with other non-memorycircuitry on a single integrated circuit.

SDRAM devices, along with other types of memory, are being implementedto conserve power consumption during operation. For example, standardSDRAM specifications describe a power-down mode which can be entered andexited while the memory device is in the active state, in response to aclock enable CKE signal. During the power-down mode, interface circuitson the device that are not necessary for detecting events needed tosignal exit from the power-down mode are deactivated by disablingdistribution of the clock signals to some of the interface circuits, andby disabling some of the receiver amplifiers and transmitter amplifiersin the interface circuits. For example, according to the DDR3 standardspecification, during power-down the input and output buffers, excludingCK, CK #, ODT, CKE and RESET #, are deactivated. In order to exit thepower-down mode, these input and output buffers need to be activated.The process of activating the interface circuits introduces a latencyfor a first memory transaction after exiting the power-down mode.Therefore, during a power-down condition, a valid, executable commandcan be applied only with power-down exit latency.

As clock rates increase, the amount of power consumed by the circuitsalso increases. In high-speed memory devices, the data clock is oftenmany times faster than the clock used for address and control signals.Thus circuits in the data clock domain consume more power.

FIG. 2 is a simplified diagram of a memory integrated circuit or memorydevice 20. Basic components of the integrated circuit include a memoryarray 21, which is accessed using a row decoder 22 and a column decoder23. Sense amplifiers 24 are coupled to the column decoder 23, andthrough the column decoder 23 to data bus circuits 25, such as buffers,multiplexers, drivers and so on. The device can include control logicand timing circuits 26 (including a command decoder) by which memoryoperations are executed. The data bus circuits 25 and the control logicand timing circuits 26 are coupled to a plurality of physical layerinterface circuits, labeled PHY 27 in the diagram. The PHY 27 provides aphysical layer interface for a plurality of data, address and controlsignals for the memory device 20. In the illustrated example, a firstset of signals includes a data clock enable DCKE, a timing signalreferred to as data clock DCK, and data DQ. A second set of signalsincludes a timing signal referred to as control clock CK, a chip selectCS, a clock enable CKE, and addresses ADDR. The PHY 27 includes acontrol clock domain 28 and the data clock domain 29. The interfacecircuits for the first set of signals (e.g., a data interface) are partof the data clock domain and process data being exchanged with thememory array, and the interface circuits for the second set of signals(e.g., a request interface) are part of the control clock domain andprocess received commands. The interface circuits in the data clockdomain 29 are coupled to the data bus circuits 25, and perform at leastone of sampling of, or transmission of, the data signals, and theinterface circuits in the control clock domain 28 are coupled to thecontrol logic and timing circuits 26, and sample command and addresssignals.

The PHY 27 includes an interface control circuit to disable a pluralityof interface circuits in the first and second domains in a power-downmode, to enable a first plurality of the interface circuits in the firstdomain in response to a first event signaling exit from the power-downmode, such as an assertion of the clock enable signal CKE, and to enablea second plurality of interface circuits in the second domain inresponse to a second event detected after activating the first pluralityof interface circuits. As mentioned above, on exit from a power-downmode, a memory operation requiring memory access will involve a memorycore latency as the command initiating the operation is decoded, and thesignals propagate through the memory core for an interval of time beforedata is delivered from the memory core to the interface circuits for aread operation, or data is distributed to the memory core from theinterface circuits for a write operation. During this memory corelatency, it may not be necessary for all of the interface circuits inthe data clock domain to be enabled. Thus, the memory device is enabledto generate or detect a second event to manage the activation of theinterface circuits in a data clock domain so that they can be enabledwith a timing different than the activation of those interface circuitsin the control clock domain in order to conserve power. In order thatthe latency for a memory operation on exit from a power-down mode is assmall as possible, the interface circuits in the control clock domainand in the data clock domain are preferably enabled within the memorycore latency, for such operations as require access to the memory core.Efficient power conservation can also be achieved by activating onlysuch interface circuits as are needed for execution of a given operationon exit from the power-down mode. Thus, for an operation that does notrequire memory core access, it may not be necessary to enable theinterface circuits in the data clock domain immediately upon exit fromthe power-down mode. Rather, such interface circuits can be enabled inresponse to commands requiring memory core access which may occur afterone or more other commands are received on exit from the power-downmode.

The second event, in response to which second domain interface circuitsare enabled, is represented in FIG. 2 by the external data clock enablesignal DCKE. A memory controller or host processor can drive theseparate clock enable pins (CKE and DCKE) for the control clock domainand the data clock domain. As discussed in more detail below, thevariety of events can act as a signal for activation of the interfacecircuits in the second domain during exit from a power-down mode.Likewise, although the clock enable signal CKE is commonly used tosignal the activation of interface circuits on memory devices duringexit from a power-down mode, other events could be utilized for thispurpose.

In this example, the data clock DCK is provided by an external source tothe memory device 20. In alternative systems, the data clock DCK isproduced on the device 20. For example, the data clock DCK can beproduced on the device 20, in response to the control clock CK usingclock divider circuits and the like.

The technology described herein allows power-down exit to be staggeredfor the two clock domains. This leads to dissipation of power in thedata portion of the PHY 27 only when data transactions are pending. Inthe DRAM field, for example, non-CAS commands (e.g. refresh, precharge,activate, etc.) can be executed without powering on data clocks in thePHY 27. The technology described here can provide flexibility to meetpower-down exit timing with minimal power penalty.

FIG. 3 is a block diagram of physical layer interface circuits 50 suchas could be implemented on a device like that of FIG. 2. In thisexample, a control clock CK from a source external to the device iscoupled to a pair 51 of pads, which in turn are coupled to a clockbuffer 52. A clock enable CKE is coupled to pad 53, which is coupled toa buffer 54. A set of command and address C/A signals are coupled torespective pads represented by pad 55, which in turn are coupled torespective buffers, represented by buffer 56. The data clock DCK from asource external to the device is coupled to a pair 57 of pads, which inturn are coupled to clock buffer 58. A set of data signals DQ arecoupled to respective pads, represented by pad 59, and to input/outputcircuitry for the corresponding pad. As illustrated in the FIG. 3, theinput/output circuitry for a pad 59 includes an input receiver buffer60, and an output transmitter buffer 61. Also, on die terminationcircuitry 62 is coupled to the pads for the data signals, including pad59.

According to the simplified diagram in FIG. 3, the command and addressC/A signals output from buffer 56 are coupled to clocked latches 71. Theclocked latches 71 are driven by the control clock CK, via clockdistribution circuitry 70. The interface circuits 50 include an on dietermination signal ODT EN which is applied by on die termination controlcircuits to a clocked latch 72. The clocked latch 72 is also driven bythe control clock CK via the clock distribution circuitry 70. The clockdistribution circuitry 70 is responsive to the clock enable CKE signalsupplied by buffer 54, to control activation and deactivation ofinterface circuits (e.g. 70, 71, 72) within the control clock domain. Ofcourse, events other than assertion of the clock enable CKE signal canbe utilized for this purpose.

The data signals DQ output from receiver buffer 60 are coupled toclocked latches 76. The clocked latches 76 are driven by the data clockDCK via data clock distribution circuitry 75. Data signals DQ applied tothe transmitter buffer 61 are provided by the output multiplexer 77,which is also clocked by the data clock DCK via the data clockdistribution circuitry 75. The data clock distribution circuitry 75 isresponsive to a power-down exit activation circuit 80 to controlactivation and deactivation of interface circuits (e.g. 76, 77, 75)within the data clock domain. The power-down exit activation circuit 80can implement a variety of logical architectures to control theactivation of interface circuits in the data clock domain at a timelater than activation of the interface circuits in the control clockdomain, such as after a time interval comprising (equal to or longerthan, and not necessarily synchronized with) a minimum number of cyclesof a selected one of the data clock (i.e. first timing signal) and thecontrol clock (i.e., second timing signal). In this way, the interfacecircuits operating in response to the high-speed data clock are notenabled prematurely, and power is conserved. The later time can bedefined as equal to or longer than at least a minimum number of clockcycles of a clock signal having a common harmonic frequency to both thedata clock (i.e., a first timing signal) and the control clock (i.e., asecond timing signal), as can be understood with reference to the timingdiagrams in FIGS. 4-7.

FIGS. 4-7 are timing diagrams that illustrate logical architectures, ormethods, for power-down exit activation which can be used in memorydevices like those described above. FIG. 4 includes timing traces forthe control clock CK, control clock enable CKE, chip select CS, thecommand an address signals CA[x:0], the data clock DCLK, an internaldata clock enable enDCK, data signals DQ(Write) for a write operationand the data signals DQ(Read) for a read operation. In this example, theclock period for the control clock (two “eyes”) can be on the order of 1to 2 nanoseconds in a modern high-speed memory device. The clock periodfor the data clock can be about one fourth that of the control clock, sothat the data clock is running at four times the speed of the controlclock. In a memory device operating with a double data rate DDR datainterface, data can be sampled on each edge of the data clock so that abit period for sampling data would be ⅛ that of the control clock periodwith a data clock that is four times faster than the control clock. Inthe example shown in FIG. 4, the clock enable CKE signal transition 100indicates an operation for exit from power-down. The chip select CSsignal transition 101 occurs within a time interval on the order of 7 to10 nanoseconds for example, allowed for activation of the interfacecircuits needed for processing the command and address signals appliedto the device. The command and address signals become active along withor upon assertion of chip select CS, as indicated by their roughalignment with the transition 101. Typical commands require more thanone command/address cycle to indicate a memory operation. Afterreceiving the sequence of commands/address cycles needed to indicate aspecific command, and decoding that sequence, power-down exit activationlogic can determine whether or not it is necessary to enable theinterface circuits in the data clock domain. If the sequence ofcommands/address cycles predict or indicate a memory core accessoperation, such as a read or write, then the logic causes the internaldata clock enable enDCK to be generated automatically at transition 102.This assertion occurs within a time interval that preferably matches thememory core latency for the memory operation predicted or indicated. Asa result, data clock distribution circuits are enabled, and theinterface circuits for the data clock domain are enabled as indicated bytransitions 103 and 104. Memory core latency for a write operation canbe different than the memory core latency for a read operation.Accordingly, an embodiment can cause the interface circuits for the dataclock domain to be enabled at times depending on whether a read or writeoperation is being executed. According to the power-down exit logicarchitecture of FIG. 4, interface circuits in the data clock domain areenabled only when needed upon exit from a power-down mode. Thisconfiguration relies on decoding a sequence of commands/address cyclesin order to provide an event indicating that the interface circuits inthe data clock domain need to be enabled. This event can only bedetected after a first latency, and the interface circuits can only beenabled after a second latency, where the first and second latencies arecharacteristic of the architecture of the memory device. It is possiblethat the memory core latency can be less than the sum of the first andsecond latencies. If this were the case, then this architecture forpower-down exit might cause an increase in memory access latency on exitfrom a power-down mode.

FIG. 5 illustrates an alternative logical architecture for power-downexit. FIG. 5 includes timing traces for the control clock CK, controlclock enable CKE, chip select CS, the command and address signalsCA[x:0], the data clock DCLK, an internal data clock enable enDCK, datasignals DQ(Write/Read) for a write or read operation. In this example,rather than relying on the decoding of a sequence of command/addresscycles, the power-down exit logic for activating the interface circuitsin a data clock domain is responsive to the transition 101 on the chipselect signal. Since this transition 101 occurs well in advance of thedecoding of the sequence of commands/address cycles, the interfacecircuits in the data clock domain can be enabled earlier. This techniquecan be used to ensure that memory access latency on exit from power-downmode does not need to be extended to account for activating theinterface circuits in the data clock domain. However, the chip selectsignal does not provide indication about whether the operation requiresa memory core access, or whether the operation is a read or writeoperation for example. Thus, it will cause activation of the interfacecircuits in the data clock domain for all of memory operations, whetheror not these interface circuits are necessary. This can cause powerconsumption in the interface circuits that is wasted.

FIG. 6 illustrates yet another alternative logical architecture forpower-down exit. FIG. 6 includes timing traces for the control clock CK,control clock enable CKE, chip select CS, the command and addresssignals CA[x:0], the data clock DCLK, an internal data clock enableenDCK, data signals DQ(Write/Read) for a write or read operation. Inthis example, rather than relying on the decoding of a sequence ofcommand/address cycles, or relying on the assertion of the chip selectsignal, the power-down exit logic for activating the interface circuitsin a data clock domain is responsive to the transition 100 on the clockenable CKE signal. Since this transition 100 occurs well in advance ofthe decoding of the sequence of commands/address cycles, and in advanceof the assertion of the chip select signal, the interface circuits inthe data clock domain can be enabled earlier. This technique can be usedto ensure that memory access latency on exit from power-down mode doesnot need to be extended to account for activating the interface circuitsin the data clock domain. However, the clock enable CKE signal does notprovide any indication about whether the operation requires a memorycore access, or whether the operation is a read or a write operation forexample. Thus, it will cause activation of the interface circuits in thedata clock domain for all of memory operations, whether or not theseinterface circuits are necessary. This can cause power consumption inthe interface circuits that is wasted.

FIG. 7 illustrates yet another alternative, illustrating the use of theexternal data clock enable DCKE signal. FIG. 7 includes timing tracesfor the control clock CK, control clock enable CKE, chip select CS, thecommand and address signals CA[x:0], the data clock DCLK, an internaldata clock enable enDCK, data signals DQ(Write) for a write operationand the data signals DQ(Read) for a read operation. Also, FIG. 6includes a trace for the data clock enable DCKE. In this example,activation logic used for asserting the internal data clock enable enDCKis responsive to the externally supplied data clock enable DCKE. TheDCKE signal is provided by an external source, such as a memorycontroller or host computer. Assertion of the DCKE signal occurs at thetransition 110 in FIG. 7, which is in advance of the assertion of thechip select CS signal. This transition 110 is produced by the externalsource at a time that allows assertion of enDCK at transition 102 tooccur at the desired time relative to the memory core latency for theread or write operation that is occurring or predicted to occur. Thetiming of the assertion of DCKE can be controlled depending on thememory operation to be executed. Also, the logic for implementation ofthe data clock activation circuits can cause an assertion of theinternal enDCK signal at a fixed time after detection of the transition110 on the DCKE signal. The sources for the DCKE signal can assert thesignal only for a memory operation that requires memory core access thatis the first in a queue for execution on exit from the power-down mode,and at the proper time for that memory operation. In this manner DCKEcan be asserted only during time periods when memory core access isrequired and can be de-asserted during other times. In other words, ifthere is a series of transactions where a few of them require DCKE to beasserted while others do not, the timing of DCKE can be adjustedaccordingly. During the assertion/de-assertion of DCKE, CKE can continueto be asserted. Therefore, the interface circuits in the data clockdomain can be enabled only when needed. Also, the inherent latenciesinvolved in relying on the decoding of a sequence of command/addresscycles are no longer a limitation on the timing of the activation of thedata domain interface circuits.

A method of operation for a memory device including a first plurality ofinterface circuits responsive to a first clock and a second plurality ofinterface circuits responsive to a second clock, can be understood withreference to these timing diagrams, which includes deactivating thefirst and second pluralities of interface circuits in a power-down mode;activating the first plurality of interface circuits in response to afirst event signaling an exit from the power-down mode; and activatingthe second plurality of interface circuits in response to a second eventdetected after activating the first plurality of circuits. The interfacecircuits in the first plurality of interface circuits can be coupled tocommand and address logic providing address and operation mode controlfor a memory core, and interface circuits in the second plurality ofinterface circuits can be coupled to data paths in the memory core. Anembodiment of the method for deactivating the first and secondpluralities of interface circuits can include disabling distribution ofthe first and second clocks, while activating the first plurality ofinterface circuits includes enabling distribution of the first clock inresponse to a first enable signal and activating the second plurality ofinterface circuits includes enabling distribution of the second clock,and wherein said event comprises detection of a second enable signalasserted after the first enable signal.

The method can include receiving a first clock enable signal from asource external to the memory at a first control signal interfacecircuit, and asserting the first enable signal in response to the firstclock enable signal; and receiving a second clock enable signal from asource external to the memory at a second control signal interfacecircuit. In this case, the method includes asserting the second enablesignal in response to the second clock enable signal provided by anexternal source.

The method can include decoding a command after activating the firstplurality of interface circuits, and asserting the second enable signalif the decoded command predicts or signals an operation using the secondplurality of interface circuits. Alternatively, the method can includereceiving a first external clock signal and a second external clocksignal at respective clock signal interface circuits from a source orsources external to the memory, and producing the first and secondclocks in response to the first external clock signal and the secondexternal clock signal, respectively.

FIG. 8 provides a more detailed logic diagram for a memory deviceincluding a physical interface with a control clock domain and a dataclock domain, that are enabled with different timing on exit from thepower-down mode. The device includes a differential input for anexternal clock CK that is coupled to amplifier 150, which remainsenabled during a power-down mode. Amplifier 150 is connected to a levelshifter 151, which translates a low swing signal at the output of theamplifier 150 to a CMOS level clock signal in this example. The outputof the level shifter 151 is applied to a first string of clock buffers152, 153 and to a second string of clock buffers 154, 155. The output ofthe clock buffer 155 is coupled to a clocked register 157 at the outputof amplifier 156. Amplifier 156 is coupled to the input pad for a clockenable signal CKE, and remains enabled during a power-down mode. Theoutput of the clocked register 157 drives a clock enable circuit 158,which outputs a global clock enable signal CKgblEn that is applied tothe buffer 152 in the first string of buffers at the output of the levelshifter 151. This causes a CK clock to be provided at the output of thebuffer 153 only after assertion of the clock enable signal CKE.

The clock at the output of the buffer 153 is applied to the eight setsof interface circuits which receive the command and address signalsC/A[5:0], the chip select CS signal and the on die termination ODTsignal in this example. Each of the eight sets of interface circuitsincludes an input amplifier 159, a clocked register 160 clocked by theCK clock from the output of buffer 153, and a divider and deserializercircuit 161 also clocked by the CK clock. In addition, the CK clock atthe output of buffer 153 is applied as a control clock to the memorycore, to command/address decoding circuits and other logic on thedevice. The amplifiers 159 in this set of interface circuits aredisabled during a power-down mode, and enabled by the signal RQEn,produced in response to the CKE signal at the output of the clockedregister 157.

FIG. 8 also illustrates a read data path including output driver 168coupled to a DQ pad on the chip. The driver 168 receives data signalsfrom the output multiplexer 169, which in turn is supplied by thedivider and serializer circuit 170. The divider and serializer circuit170 coupled to the memory core 140 receive read data. A write data pathis not shown in the drawing, but can have a similar, complementarystructure.

The device in FIG. 8 also includes a differential input for an externaldata clock DCK that is coupled to amplifier 165. The output of theamplifier 165 is applied to clock distribution circuits which in thisexample include a current mode logic buffer 167. The output of thecurrent mode logic buffer 167 is applied to a level shifter 171 (lowswing to CMOS in this example) to produce a DCK clock that is applied tothe divider/deserializer circuit 170 and to the output multiplexer 169.A transmit enable signal TxEn is used to enable the driver 168 and thelevel shifter 171. The transmit enable signal TxEn is produced bycommand/address decoder 162.

An internal data clock enable enDCK signal is used to enable theamplifier 165, and the current mode logic buffer 167 on exit from apower-down mode. The enDCK signal is generated by the data clock enablelogic 166 that executes a logic architecture, such as those describedabove with reference to FIGS. 4 through 7, and can be responsive to oneor more signals or events that are detectable on the device.

FIG. 8 illustrates a path 300 which heuristically demonstrates a memoryaccess latency on exit from power-down, and a path 301 whichheuristically demonstrates the data clock activation latency. The memoryaccess latency path 300 includes components that are derived from thepropagation of command/address signals through amplifier 159 and otherinterface circuits through the command/address decoder 162 to the memorycore 140, and then out of the memory core through the transmit pathinterface circuits (168, 169, 170) for the data. The data clockactivation latency path 301 includes components that are derived frompropagation of the signals corresponding to the events that drive thelogic 166, through the amplifier 165, the current mode logic buffer 167,level shifter 171 and the interface circuits (160, 169, 170) for thedata. As mentioned above, it is desirable that the data clock activationlatency be aligned with the memory access latency, so that the interfacecircuits in the data clock domain are not enabled too early and wastepower, and are not enabled unnecessarily in anticipation of memoryoperations that do not involve the data path.

FIG. 9 illustrates an alternative implementation; where the componentsmatching those of FIG. 8 are given the same reference numbers and notdescribed again. In this example, the device includes a DCKE input padwhich is coupled to amplifier 180. The output of the amplifier 180 isapplied to a clocked register 181, which is clocked by the CK clock fromthe output of buffer 153 like the command/address path interfacecircuits. Although not illustrated in this example, the amplifier 180can remain active during the power-down mode, or, in an alternativeembodiment, the RQEn signal or other enable signal can be used todisable the amplifier 180 during power-down, and to enable it on exitfrom the power-down mode. The output of the clocked register 181 isapplied to the data clock enable logic 182. The data clock enable logic182 produces the internal data clock enable enDCK with the desiredtiming as described above with reference to FIG. 7.

FIG. 9 illustrates a path 311 which heuristically demonstrates the dataclock activation latency. The data clock activation latency path 311includes components that are derived from propagation of the DCKE signalvia amplifier 180, clocked register 181, the data clock enable logic182, and through the amplifier 165, the current mode logic buffer 167,level shifter 171 and the interface circuits (160, 169, 170) for thedata. As described above, because the timing of the DCKE signal can becontrolled externally, this embodiment allows for efficient control ofthe timing of the activation of the interface circuits in the data clockdomain.

FIG. 10 illustrates an alternative implementation, where the componentsmatching those of FIG. 8 are given the same reference numbers and notdescribed again. In this example, a command/address decoder 190 isimplemented to detect memory operations requiring memory core access onexit from power-down, and to produce the enDCK as needed, as describedabove with reference to FIG. 4. FIG. 10 illustrates a path 321 whichheuristically demonstrates the data clock activation latency. The dataclock activation latency path 321 includes components derived from thepropagation of command/address signals through amplifier 159 and otherinterface circuits through the command/address decoder 190, and throughthe amplifier 165, the current mode logic buffer 167, level shifter 171and the interface circuits (160, 169, 170) for the data.

In one approach to implementation, the command/address decoder 190 asshown in FIG. 10 can be adapted to detect a “short command,” which canbe inserted in a command sequence and detected as an event used forsignaling activation of the data domain interface circuits on exit frompower-down. A representative memory device may include a command packetthat requires a four cycle sequence of commands/address opcodes andaddress bits to indicate a particular memory operation. This four cyclesequence introduces latency into the data domain activation logic asdiscussed above. The “short command” can be used which may comprise oneor two cycles, which can be decoded with less latency than a full reador write command packet. This would require inserting a look-aheadpacket, which could comprise a single cycle opcode, into the commandstream during an exit from power-down.

FIG. 11 illustrates a command sequence executed on exit from power-down,which includes a first command CMD1 including a four cycle packet (or asequence of N command/address cycles), which could be an activatecommand or other command not requiring memory core access. The firstcommand CMD1 is followed by a short command CAX that comprises one cycle(or fewer than N cycles) which acts as a look-ahead indicating a memorycore operation is upcoming and to be specified by a later command, suchas the second command CMD2, third command CMD3, or another latercommand. In one example, the third command CMD3 initiates a read or awrite operation or another operation that requires activation of thedata clock. The second command CMD2 may be directed to a differentmemory device, or be a command that does not require activation of thedata clock. A command/address decoder 190 like that of FIG. 10, detectsthe short command CAX in advance of the third command CMD3 in thisexample, enabling the activation of the data domain interface circuitsearlier during the memory operation specified by the third command CMD3,decoupling the activation latency for the data domain interface circuitsfrom the decoding of the command specifying their use.

FIG. 12 illustrates an alternative command sequence executed on exitfrom power-down, which includes a first command CMD1 including a fourcycle packet (or a sequence of N command/address cycles), which could bean activate command or other command not requiring memory core access.The first command CMD1 is followed by a second command CMD2 thatcomprises an alternate form implemented for example by setting a flag inone of the cycles of the command, such as first cycle CA1*, indicatingthat a memory core operation is upcoming and to be specified by thethird command CMD3, or by another later command. In one example, thethird command CMD3 initiates a read or a write operation or anotheroperation that requires activation of the data clock. The second commandCMD2, including the alternate form, may initiate a different operationthat does not require data clock activation. A command/address decoder190 like that of FIG. 10, detects the alternative command in advance ofthe third command CMD3 in this example, enabling the activation of thedata domain interface circuits earlier during the memory operationspecified by the third command CMD3, decoupling the activation latencyfor the data domain interface circuits from the decoding of the commandspecifying their use.

In some systems, the second command CMD2 in the sequence shown in FIG.12 can be the operation that requires data clock domain activation wherethe decoding latency is short enough for the particular embodiment. Thealternate form of the command sequence can be used to initiate theactivation of the data clock domain, along with a read, write or otheroperation.

FIG. 13 illustrates an example memory system including four ranks ofmemory devices, rank 0-rank 3, with a memory controller 982 and a sharedsignaling bus, including a command/address line 950 connected betweenthe memory controller 982 and one or more memory devices 951-954 in themultiple ranks on the module. In the configuration shown in FIG. 13,each of the memory devices 951-954 within each rank, rank 0-rank 3,receives a separate data clock enable signal DKE0 to DKE3 on respectivelines 956-0 to 956-3. The lines 956-0 to 956-3 can be implemented asseparate physical signaling lines as shown for example in the embodimentof FIG. 9, or as logical channels communicated via shared physicalsignaling lines, as discussed with reference to FIGS. 10-12. The memorycontroller 982 includes logic for asserting the individual DKE0 to DKE3signals to the memory devices 951-954, with proper timing, interleavedamong the command sequences for the target devices. Of course, thetechnology is extendable to any number of ranks, and to other memorysystem configurations.

With reference to the multi-rank embodiment, it can be understood thatthe power conservation modes utilized for integrated circuits withmultiple clock domains can include modes based on management for theclock enable signals that do not cause power down of the devices. Forexample, in the multi-rank embodiment having N ranks, thecommand/address bus can be shared among the ranks of devices. In thiscase, any one device controls the bus for only 1/N of the total cycles.So, a power conservation mode can be utilized that enables and disablesthe data clock domain as needed for the individual ranks while thecontrol clock domain remains enabled for other operations, such as forexample arbitration of access to the bus.

In examples described above, the command/address channels arepacketized. In other embodiments, commands and addresses can deliveredover separate channels. Also, discrete signals lines can be used forsome or all of the commands. For example, a command, address, andcontrol path with discrete signals, each with a specific function(similar to that of the DDR3 standard specification) could also beemployed.

A memory device described herein includes a physical layer interfacehaving a first clock domain and a second clock domain, circuits thatenable the first clock domain during exit from a power-down mode, andcircuits that enable the second clock domain after the first clockdomain is enabled during exit from the power-down mode. The first clockdomain can include interface circuits coupled to a command and addresspath in the memory, and the second clock domain can include interfacecircuits coupled to a data path in the memory. The memory device ischaracterized by a memory core latency for a read or write on exit froma power-down mode, and in embodiments described herein, the eventcausing activation of the data clock domain interface circuits occurs ata time such that the activating of the data clock domain interfacecircuits is completed within the memory core latency. The memory caninclude a first input interface for a first clock enable signal (e.g.CKE) and a second input interface for a second clock enable signal (e.g.DCKE) from an external source or sources. The circuits that enable thefirst clock domain are responsive to the first clock enable signal, andthe circuits that enable the second clock domain are responsive to thesecond clock enable signal. Alternatively, the memory device can includea command decoder coupled to the first clock domain; and a first inputinterface for a first clock enable signal (e.g. CKE) from an externalsource or sources, wherein the circuits that enable the first clockdomain are responsive to the first clock enable signal, and the circuitsthat enable the second clock domain are responsive to the commanddecoder.

It should be noted that the various circuits disclosed herein may bedescribed using computer aided design tools and expressed (orrepresented), as data and/or instructions embodied in variouscomputer-readable media, in terms of their behavioral, registertransfer, logic component, transistor, layout geometries, and/or othercharacteristics. Formats of files and other objects in which suchcircuit expressions may be implemented include, but are not limited to,formats supporting behavioral languages such as C, Verilog, and VHDL,formats supporting register level description languages like RTL, andformats supporting geometry description languages such as GDSII, GDSIII,GDSIV, CIF, MEBES and any other suitable formats and languages.Computer-readable media in which such formatted data and/or instructionsmay be embodied include, but are not limited to, computer storage mediain various forms (e.g., optical, magnetic or semiconductor storagemedia, whether independently distributed in that manner, or stored “insitu” in an operating system).

When received within a computer system via one or more computer-readablemedia, such data and/or instruction-based expressions of the abovedescribed circuits may be processed by a processing entity (e.g., one ormore processors) within the computer system in conjunction withexecution of one or more other computer programs including, withoutlimitation, net-list generation programs, place and route programs andthe like, to generate a representation or image of a physicalmanifestation of such circuits. Such representation or image maythereafter be used in device fabrication, for example, by enablinggeneration of one or more masks that are used to form various componentsof the circuits in a device fabrication process.

In the foregoing description and in the accompanying drawings, specificterminology and drawing symbols have been set forth to provide athorough understanding of the present invention. In some instances, theterminology and symbols may imply specific details that are not requiredto practice the invention. For example, any of the specific numbers ofbits, signal path widths, signaling or operating frequencies, componentcircuits or devices and the like may be different from those describedabove in alternative embodiments. In other instances, well-knowncircuits and devices are shown in block diagram form to avoid obscuringthe present invention unnecessarily. Additionally, links or otherinterconnection between integrated circuits or internal circuit elementsor blocks may be shown as buses or as single signal lines. Each of thebuses may alternatively be a single signal line, and each of the singlesignal lines may alternatively be buses. Signals and signaling links,however shown or described, may be single-ended or differential. Asignal driving circuit is said to “output” a signal to a signalreceiving circuit when the signal driving circuit asserts (or deasserts,if explicitly stated or indicated by context) the signal on a signalline coupled between the signal driving and signal receiving circuits.The term “control clock” is used herein simply for the purpose ofdistinguishing the clock from the “data clock.” No specific controlfunction is implied by the name “control clock.” The term “coupled” isused herein to express a direct connection as well as a connectionthrough one or more intervening circuits or structures. Integratedcircuit “programming” may include, for example and without limitation,loading a control value into a register or other storage circuit withinthe device in response to a host instruction and thus controlling anoperational aspect of the device, establishing a device configuration orcontrolling an operational aspect of the device through a one-timeprogramming operation (e.g., blowing fuses within a configurationcircuit during device production), and/or connecting one or moreselected pins or other contact structures of the device to referencevoltage lines (also referred to as strapping) to establish a particulardevice configuration or operation aspect of the device. The terms“exemplary” and “embodiment” are used to express an example, not apreference or requirement.

While the invention has been described with reference to specificembodiments thereof, it will be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope. For example, features or aspects of any of the embodimentsmay be applied, at least where practicable, in combination with anyother of the embodiments or in place of counterpart features or aspectsthereof. Accordingly, the specification and drawings are to be regardedin an illustrative rather than a restrictive sense.

What is claimed is:
 1. A method of operation within anintegrated-circuit memory component (“memory IC”), the methodcomprising: receiving, via a first clock input, a command/address clocksignal that toggles continuously throughout a first interval at a firstfrequency; receiving, via a second clock input, a data clock signal thattoggles at a second frequency at least twice the first frequency; duringan initial portion of the first interval while distribution of the dataclock signal within a data interface is disabled, receiving a memoryaccess command synchronously with respect to the command/address clocksignal; and enabling distribution of the data clock signal within thedata interface of the memory IC during a latter portion of the firstinterval in response to receiving the memory access command.
 2. Themethod of claim 1 wherein enabling distribution of the data clock withinthe data interface comprises enabling execution, within the datainterface, of either a write data reception operation specified by thememory access command or a read data transmission operation specified bythe memory access command.
 3. The method of claim 1 wherein enablingdistribution of the data clock signal within the data interface of thememory IC comprises conducting the data clock signal to timing inputs ofat least one of data reception circuitry or data transmission circuitrywithin the data interface.
 4. The method of claim 1 further comprisingmaintaining a data-clock-enable signal in a deasserted state during theinitial portion of the first interval to disable distribution of thedata clock signal within the data interface, and wherein enablingdistribution of the data clock signal within the data interfacecomprises asserting the data-clock-enable signal in response toreceiving the memory access command.
 5. The method of claim 1 whereinenabling distribution of the data clock signal within the data interfaceof the memory IC in response to receiving the memory access commandcomprises enabling distribution of the data clock signal a predeterminedtime after receiving the memory access command.
 6. The method of claim 1wherein receiving the memory access command comprises receiving acommand that specifies a data transfer via the data interface, themethod further comprising receiving, during the initial portion of thefirst interval and prior to receiving the memory access command, acommand to perform a first operation within the memory IC withouttransferring data via the data interface, and responsively performingthe first operation without enabling distribution of the data clocksignal within the data interface.
 7. The method of claim 6 wherein thefirst operation comprises at least one of a memory refresh operation, arow activation operation or a row precharge operation.
 8. The method ofclaim 1 wherein enabling distribution of the data clock signal withinthe data interface comprises asserting a data-clock-enable signal, themethod further comprising receiving a data clock control command thatinstructs the memory IC to set the data-clock-enable signal to apredetermined state.
 9. The method of claim 1 wherein receiving thememory access command comprises receiving the memory access commandsynchronously with respect to the command/address clock signal duringassertion of a clock-enable signal at a clock-enable input of the memoryIC.
 10. The method of claim 1 wherein the data clock signal toggles atthe second frequency continuously throughout the first interval.
 11. Anintegrated-circuit memory component (“memory IC”) comprising: a firstclock input to receive a command/address clock signal that togglescontinuously throughout a first interval at a first frequency; a secondclock input to receive a data clock signal that toggles at a secondfrequency at least twice the first frequency; a command/addressinterface to receive, during an initial portion of the first intervalwhile distribution of the data clock signal within the data interface isdisabled, a memory access command synchronously with respect to thecommand/address clock signal; and control circuitry to enabledistribution of the data clock signal within the data interface of thememory IC during a latter portion of the first interval in response toreceiving the memory access command.
 12. The memory IC of claim 11wherein the control circuitry to enable distribution of the data clockwithin the data interface comprises circuitry to enable execution,within the data interface, of either a write data reception operationspecified by the memory access command or a read data transmissionoperation specified by the memory access command.
 13. The memory IC ofclaim 11 wherein the control circuitry to enable distribution of thedata clock signal within the data interface comprises circuitry toconduct the data clock signal to timing inputs of at least one of datareception circuitry or data transmission circuitry within the datainterface.
 14. The memory IC of claim 11 wherein the control circuitryto enable distribution of the data clock signal within the datainterface comprises circuitry to maintain a data-clock-enable signal ina deasserted state during the initial portion of the first interval todisable distribution of the data clock signal within the data interfaceand to assert the data-clock-enable signal in response to receiving thememory access command.
 15. The memory IC of claim 11 wherein the controlcircuitry to enable distribution of the data clock signal within thedata interface in response to receiving the memory access commandcomprises circuitry to enable distribution of the data clock signal apredetermined time after receiving the memory access command.
 16. Thememory IC of claim 11 wherein the memory access command specifies a datatransfer via the data interface, and wherein the command/addressinterface is further to receive, during the initial portion of the firstinterval and prior to receiving the memory access command, a command toperform a first operation within the memory IC without transferring datavia the data interface, and wherein the control circuitry comprisescircuitry to perform the first operation without enabling distributionof the data clock signal within the data interface.
 17. The memory IC ofclaim 11 wherein the control circuitry to enable distribution of thedata clock signal within the data interface comprises circuitry to (i)assert a data-clock-enable signal in response to reception of the memoryaccess command via the command/address interface, and (ii) set thedata-clock enable signal to a predetermined state in response toreception, via the command/address interface, of a data clock controlcommand that specifies the predetermined state.
 18. The memory IC ofclaim 11 further comprising a clock-enable input, and wherein thecommand/address interface is to receive the memory access commandsynchronously with respect to the command/address clock signal duringassertion of a clock-enable signal at the clock-enable input.
 19. Thememory IC of claim 11 wherein the data clock signal toggles at thesecond frequency continuously throughout the first interval.
 20. Anintegrated-circuit memory component (“memory IC”) comprising: means forreceiving a command/address clock signal that toggles continuouslythroughout a first interval at a first frequency; means for receiving adata clock signal that toggles at a second frequency at least twice thefirst frequency; means for receiving, during an initial portion of thefirst interval while distribution of the data clock signal within thedata interface is disabled, a memory access command synchronously withrespect to the command/address clock signal; and means for enablingdistribution of the data clock signal within the data interface of thememory IC during a latter portion of the first interval in response toreceiving the memory access command.